The present invention relates to a lead frame and a material of the same made of a Cu alloy.
Recently, the improvement of materials used for integrated circuits (IC) has made rapid progress, allowing highly integrated and mass-produced IC. In many fields, both material and components are required to be further improved because of the concern about properties and price.
For example, a lead frame made of a Fe-Ni alloy such as 42 wt % Ni-Fe or 29 wt % Ni-17 wt % Co-Fe has a coefficient of thermal expansion very similar to that of the semiconductor element.
However, a lead frame made of a Fe alloy is expensive because expensive components such as nickel and cobalt are used. In addition, a lead frame made of a Fe alloy doesn't satisfy the requirements of high radiation, that is, thermal conductivity, which is required as semiconductors become highly integrated.
Accordingly, lead frames made of a Cu alloy are chiefly being used because of the property of high radiation and relative inexpensiveness. In such lead frames made of a Cu alloy, Cu-Cr-Zr alloy is especially being used because of its high hardness and high conductivity.
However, the lead frame made of a Cu-Cr-Zr alloy as described above often has a peeling part on the surface of the lead frame, and a plating scab caused by heat treatment when the surface is coated. When an IC package or a LSI package with a lead frame of Cu-Cr-Zr alloy is made, because of the problems as described above, the yield of production and the reliability of these packages of a Cu-Cr-Zr alloy are impaired. Further more, a Cu-Cr-Zr alloy as described above is required to have high conductivity with a good producibility, for example not less than 75IACS %, for the high efficiency of a lead frame.